1. Field of the Invention
The present invention relates to an automotive headlamp in which a light source unit is tilted about a predetermined tilting center axis by means of an optical axis adjustment mechanism interposed between a housing and the light source unit mounted in front of the housing so as to adjust (aim) the optical axis of the light source unit in a tilting fashion. More particularly, the present invention relates to an automotive headlamp including a synthetic resin nut member fittingly screwed on to an adjusting screw which is rotatably supported on the housing and mounted on the light source unit in such a manner as to interlock with the rotation of the adjusting screw for forward or backward movement so as to tilt the light source unit about a tilting center axis which passes through the tilting fulcrum.
2. Related Art
FIGS. 11 to 13 show one type of an automotive headlamp including a light source unit 22 having a light source 2b integrated into a reflector 2a. The light source unit 22 is supported on a front side of a lamp body 1 by an aiming mechanism. The aiming mechanism includes a ball and socket joint 3, which constitutes a tilting fulcrum, two aiming screws 4, 5 and two nut members 6, 7 which are thread fitted, respectively, on the aiming screws 4, 5 and forwardly and backwardly movable. The nut members 6, 7 constitute movable tilting fulcrums.
Namely, the synthetic resin nut member 6 (7), which is securely mounted on a bracket 2c (2d) of the light source unit 2 via a bearing 8, is thread fitted on the aiming screw 4 (5) which is rotatably supported on the lamp body 1 and which extends forwards. A leaf spring slide portion 6a (7a) is integrally formed on the nut member 6 (7) in such a manner as to be brought into an elastic engagement with a guide portion 9 provided on the lamp body 1 in such a manner as to extend longitudinally so as to carry thereon the nut member 6 (7). Then, by rotating the aiming screw 4 (5), the nut member 6 (7) moves forwards or backwards along the aiming screw 4 (5), and the light source unit 2 is tilted about a tilting center axis which passes through the ball and socket joint 3, whereby the optical axis of the lamp can be tilted and panned vertically and horizontally for adjustment.
In addition, the ball and socket joint 3 is made up of a slider 3a of an automatic headlight leveling actuator which moves forwards or backwards and a bearing 3b which is mounted on a bracket 2e of the light source unit 2 and makes up an automatic headlight leveling mechanism in which the slider 3a operates to move forwards or backwards according to a change in the inclination angle of the vehicle axis of an automotive vehicle in the longitudinal direction, whereby the light source unit 2 is tilted about a horizontal tilting center axis which passes through the nut members 6, 7. Note that a ball bearing portion 8a is provided on the bearing 8 for rotatably supporting a ball portion 6b (7b) of the nut member 6 (7) so as to avoid an unanticipated generation of stress on a mounting portion between the nut member 6 (7) and the light source unit 2 when the light source unit 2 is tilted.
Then, the bearing 8 and the nut member 6 (7) are made of a synthetic resin (for example, polyacetal resin) which is superior in sliding properties and resistance to wear in consideration of sliding properties and resistance to wear between the bearing 8 and the nut member 6 (7) and sliding properties and resistance to wear between the slide portion 6a (7a) and the guide portion 9.
In the automotive headlamp described above, however, when the aiming mechanism and the automatic headlight leveling mechanism are used for, in particular, a long period of time, a looseness is generated in the screw thread fitting portion of the nut member 6 (7) into which the aiming screw 4, (5) is thread fitted. As a result, there is a case that the optical axis of the lamp deviates independently.